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.TH MKINITRD 8 "11 May 2007" "Slackware Version 12.0"
.SH NAME
mkinitrd \- create or rebuilt an initrd (initial ramdisk) using initramfs (simple cpio+gzip).
.SH SYNOPSIS
.B mkinitrd
[
.B \-c
]
[
.B \-f filesystem
]
[
.B \-k kernel_version
]
[
.B \-m module1:module2:module3...
]
[
.B \-o output_file
]
[
.B \-r root_device
]
[
.B \-s source_tree
]
[
.B \-C
]
[
.B \-L
]
[
.B \-V
]
.SH DESCRIPTION
.SH DESCRIPTION
.B mkinitrd
is used to build an initial ramdisk.  An initial ramdisk is a very small set of files
that are loaded into RAM and "mounted" (as initramfs doesn't actually use a filesystem) as the kernel boots (before the main root filesystem is mounted).  The usual reason to use an initrd
is because you need to load kernel modules before mounting the root partition.
Usually these modules are
required to support the filesystem used by the root partition (ext3,
reiserfs, xfs), or perhaps the controller that the hard drive is attached
to (SCSI, RAID, etc).  Essentially, there are so many different options
available in modern Linux kernels that it isn't practical to try to ship
many different kernels to try to cover everyone's needs.  It's a lot more
flexible to ship a generic kernel and a set of kernel modules for it. 
.SH OPTIONS
.TP
.B \-c
Clear the existing initrd tree (by default in /boot/initrd-tree/) first.
If this is not done, running mkinitrd will add additional modules to the
existing initrd.
.TP
.B \-f filesystem
Specify the filesystem to use for the root partition.  If this isn't given,
mount will usually figure it out.  This option must be used together with the
\-r option in order to be beneficial.
.TP
.B \--help
Display a help summary.
.TP
.B \-k kernel version
Use kernel modules from the specified kernel version.  mkinitrd will look for them in
/lib/modules/(kernel version).
.TP
.B \-m module list
This is a list of colon-delimited modules to build into the initrd.
Any dependencies of requested modules will also be added to the initrd.
Additional options may be added to use when loading the kernel modules
(but in this case the entire list must be wrapped with double quotes). 
.TP
.B \-o output image
The file to write the initrd to.  (default: /boot/initrd.gz)
.TP
.B \-r root partition
Specify the device to be used as the root partition.  If this isn't given, the
kernel default will be used (which is usually fine).  This option must be used
together with the \-f option in order to be beneficial.
.TP
.B \-s source tree
The directory to use as the source for the initrd.  (default: /boot/initrd-tree/)
.TP
.B \-C
Use cryptsetup to enable the underlying device of an encrypted root partition.
Requires '-r' parameter with the *mapped* device name as an argument, like this:
.PP
  -C /dev/sda2 -r cryptroot
.PP
where the actual root device name in /etc/fstab is:
.PP
  /dev/mapper/cryptroot
.TP
.B \-L
This option adds LVM support to the initrd, if the tools are
available on the system.
.TP
.B \-V
Display version information and exit.
.SH EXAMPLES
A simple example:  Build an initrd for a reiserfs root partition:

  mkinitrd -c -m reiserfs

Another example:  Build an initrd image using Linux 2.6.21.3 kernel
modules for a system with an ext3 root partition on /dev/hdb3:

  mkinitrd -c -k 2.6.21.3 -m ext3 -f ext3 -r /dev/hdb3

If run without options, mkinitrd will rebuild an initrd image using
the contents of the $SOURCE_TREE directory, or, if that directory
does not exist it will be created and populated, and then mkinitrd
will exit.  These options are handy for building an initrd mostly
by hand.  After creating /boot/initrd-tree/, you can add modules and
edit files by hand, and then rerun mkinitrd to create the initrd.

Once the initrd is created, you'll need to tell your boot loader
to load it.  If you boot with LILO, you will need to add an initrd
line to /etc/lilo.conf.  Here's a section of lilo.conf that shows
how to set this up:

 # Linux bootable partition config begins
 image = /boot/vmlinuz-generic-2.6.21.3
   initrd = /boot/initrd.gz
   root = /dev/hda6
   label = Linux26213
   read-only
 # Linux bootable partition config ends

Once you've created the initrd and editing /etc/lilo.conf, you will
need to run 'lilo' to write out the changed boot block.  The next
time you reboot the initrd should be loaded along with the kernel.

Have fun!
.SH AUTHOR
Patrick J. Volkerding <volkerdi@slackware.com>
